It is known that water can be eliminated from certain wet surfaces by bringing the wet surfaces into contact with dense organic liquids immiscible with water. These liquids generally contain a surface-active agent to displace the water, which floats on the surface of the liquid. The organic liquid is brought in contact with the surfaces to be treated, for example, by spraying, by application with a brush, by sprinkling or by immersion of the surfaces in the liquid. In the latter case, which is used in the majority of industrial installations, it is advantageous to stir the liquid bath by boiling, by mechanical means or by ultrasonic means.
The fluorinated demoisturizing solvent customarily used for the displacement of water from the surface of articles is trichloro-1,1,2-trifluoro-1,2,2-ethane containing one or more surfactants. It is generally preferred to use the surface-active agents at concentrations on the order of 0.01 to 1% by weight. The prior art teaches that the displacement of water by dense liquids containing surface-active agents is carried out by adsorption of the surface-active agent on the surfaces to be demoisturized in order to render them unwettable by water. The water is then collected in the form of droplets which rise to the surface and form a separable water layer.
French Pat. No. 1,541,592 describes a continuous demoisturizing process and arrangement which consists of bringing the articles in contact with the demoisturizing liquid by immersion of the articles in a turbulent zone of a bath, allowing the water displaced to float on the surface of the displacement liquid in a rest zone in the same bath and then separating the displaced water from the demoisturizing liquid. The demoisturizing solvent used in that process has been described in French Pat. No. 1,515,393 and consists of trichloro-1,1,2-trifluoroethane containing 0.5 to 3% by weight of a surface-active agent obtained by neutralizing a mixture of mono- and dialkyl phosphates with a saturated aliphatic amine, in particular, ethyl-2-hexylamine octylphosphates. That water displacement liquid does not, however, prove fully satisfactory and other types of surfactants have been recommended. Thus, French Pat. No. 2,040,733 describes the use of amine salts of N-oleyl-propylenediamine dioleate type as surface-active agents and French Pat. No. 2,205,562 describes the use of diamides of dioleyl-oleylamidopropylene amide type. French Pat. No. 2,217,045 describes the use of cationic surfactants derived from imidazoline. The compositions containing one of the latter three types of surface-active agents yield satisfactory results on drying, but present the disadvantage of forming an emulsion when they are mixed with water. Such emulsions are difficult to separate and the separation also takes place very slowly. That characteristic considerably reduces their practical usefulness, particularly in the case of a continuous drying process, in the course of which the demoisturizing composition is recycled.
A good demoisturizing composition must respond to at least the following three criteria:
(1) The composition must efficiently dry objects of various kinds. It must be suitable for metal objects, for surfaces of glass or refractory materials and for precious stones, as well as for plastics not attackable by those compositions. The elimination or displacement of water must be as rapid and as complete as possible. PA0 (2) The demoisturizing composition must not form any emulsion on being brought in contact with water or, if such is not the case, the emulsion formed must be easily and rapidly separable into two phases. This criterion is very important, for in case of the formation of an emulsion which is difficult to separate into two phases, elimination of the aqueous layer in the course of the drying process would be very difficult and would entail the risk of carrying away a part of the demoisturizing composition emulsified in the water. PA0 (3) In order to prevent the demoisturizing composition from being diminished in the course of the operation, it is very important that the surface-active agent not be extracted with the water or for that extraction to be very slight. It is thus highly desirable for the surfactant to have a greater affinity for the halogenated solvent than for water.
U.S. Pat. No. 4,182,687 describes a demoisturizing composition which responds to those three criteria. That composition consists of a fluorochlorocarbon, and mainly trichloro-1,1,2-trifluoro-1,2,2-ethane, containing a surface-active agent, whose cationic moiety has a formula: ##STR3## in which: m=2 or 3
n=1 or 2 PA1 m+n=4 PA1 R=an alkyl group of C.sub.6 to C.sub.18 PA1 R'=an alkyl group of C.sub.1 to C.sub.2 PA1 R'=an alkyl group of C.sub.1 to C.sub.2. PA1 fritted glass drying test PA1 emulsification test PA1 water extractability test.
The anionic moiety of the formula of the surface-active agent can be varied, but the authors discovered that there is a correlation between the dimensions of the anionic moiety and the values of m and n i.e., the dimensions of the cationic moiety. Anions as different as halides, alkylphosphates, alkylcarboxylates, alkyl- or arylsulfonates, alkylsulfates or sulfosuccinates are usable, but the best results have been obtained with mono- and dialkyl phosphates. It has, furthermore, been shown that although the water displacement properties are generally good for any pair of cations and anions, a composition with good resistance to extraction of the surfactant with water, and not forming an emulsion in the course of use, can be obtained only with certain cation-anion pairs. Thus, in the case of the preferred anions in the above-mentioned patent, i.e., the mixtures of mono- and dialkyl phosphates: ##STR4## the radical R" is an alkyl group of C.sub.1 to C.sub.18, when m=3, and an alkyl group of C.sub.8 to C.sub.18, when m=2. The preferred products of the above-mentioned patent are the compositions containing a surface-active agent responding to the formulas: ##STR5## and several examples of that patent show that the hexylphosphates (Ex. 27) or the butylphosphates (Ex. 26, 28, 32) of the same quaternary ammonium or of the same type of quaternary ammonium (m=2) are not usable, for these compositions form emulsions with water that are very difficult to separate into two phases. Since the surface-active agent specially used in the compositions described in that patent is not a readily available industrial product, the patentee showed that it can be formed in situ from commercial products according to the following equation: ##STR6## A composition containing stoichiometric quantities of quaternary ammonium hydrochloride, octylphosphate and octylamine thus yields the same results in the course of the drying process as a composition solely containing quaternary ammonium octylphosphate.